The present invention relates to a partial collective mask for charged particle beam exposure implementing the collective transfer of a plurality of desired patterns.
A high throughput is the prerequisite with the production of modern semiconductor devices. This is also true with lithography for forming fine patterns in a semiconductor wafer. To realize a high throughput, there has been proposed a transfer procedure using a charged particle beam mask equivalent to a mask or a reticle formed with a desired pattern beforehand and adapted for light or X rays. A partial collective mask for this kind of transfer procedure and adapted for a charged particle beam is usually formed with openings for variable shaping and openings representative of contact patterns, line-and-space patterns or similar repetitive patterns derived from device design data.
To produce the partial collective mask, a silicon (Si) wafer as thick as 20 .mu.m has customarily been subjected to trench etching so as to form device patterns or openings. However, the problem is that the patterns to be formed in the mask each need a particular etching time in accordance with the area of its opening. It is a common practice to enhance the shaping accuracy by optimizing the composition and flow rate of a gas, etching time and so forth. The opening areas of device patterns sometimes differ from each other by 70% or more. This, coupled with the fact that differences between etching conditions in the wafer plane are not negligible, brings about a scatter in the size of the pattern or opening. Therefore, when the pattern or opening has a size smaller than a designed size, there occur various faults including the defective draw of contacts and defective partial-collective connection; in the worst case, snapping and other critical faults occur. The mask cannot be corrected in shape even in the event of such a critical fault.